The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
The present invention relates generally to gas turbine engines and more specifically to an apparatus for injecting high frequency perturbations into the flow of jet engine exhaust gasses to provide noise suppression and temperature reduction.
This application is somewhat related to my copending and commonly assigned patent applications xe2x80x9cHIGH FREQUENCY PULSED FUEL INJECTORxe2x80x9d, AFD 00436, Serial Number 09/973,161 and xe2x80x9cAIRCRAFT WEAPONS BAY HIGH FREQUENCY ACOUSTIC SUPPRESSION APPARATUSxe2x80x9d, AFD 00439, Serial Number 09/973,175, now U.S. Pat. No. 6,446,904 filed on even date herewith. The contents of these even filing date applications are hereby incorporated by reference herein.
A serious problem associated with the use of jet engines in aircraft and other applications such as stationary power generation is the propensity of the jet engine to generate high levels of noise. The noise levels generated by jet aircraft can be great enough to cause fatigue of structural members and in general create noise pollution problems in populated areas near airports. Moreover, the intense levels of noise generated create hazardous conditions for personnel working near operating jet engines. Not only is noise generation a problem, but the enormous heat expelled by the engine presents a problem for airport personnel working nearby as well.
Numerous approaches have been made to date in order to suppress jet engine noise. Representative of one of these approaches is U.S. Pat. No. 5,884,472 to Presz Jr. et al which discloses a ring of inwardly projecting lobes or projections mounted within the exhaust nozzle/tailpipe. The intent of devices such as these is to create mixing within the flow of exhaust gasses by the provision of the lobes. Another approach is found in U.S. Pat. No. 3,982,696 to Gordon disclosing a noise suppressor nozzle including several chutes for directing a flow of air into the stream of exhaust gasses at the boundary layer. Another approach similar to Gordon""s is found in U.S. Pat. No. 4,280,587 to Bhat disclosing the use of lobes, tubes or deflectors within the exhaust nozzle to promote mixing of ambient air within the flow of exhaust gasses. While each of these approaches have met with some degree of success, each presents the disadvantage of imparting a reduction in the cross sectional area of the exhaust flow, partially blocking the exhaust flow. Another disadvantage lies in the fact that these lobes and deflectors must be fabricated from very expensive, high temperature resistant materials.
A need exists therefore for an improved jet noise suppressor. Such a suppressor would exhibit improved noise suppression characteristics enhancing aircraft operation without impeding engine operation.
Accordingly, it is a primary object of the present invention to provide a jet noise suppressor overcoming the limitations and disadvantages of the prior art.
It is yet another object of the present invention to provide a jet noise suppressor that is self actuating and contains no moving parts.
Another object of the present invention is to provide jet noise suppressor providing noise reduction over a wide range of aircraft operating conditions.
It is yet another object of the present invention to provide a jet noise suppressor that can be utilized on a wide variety of aircraft.
It is still another object of the present invention to provide a jet noise suppressor that reduces exhaust gas temperature.
Still another object of the present invention is to provide a jet noise suppressor that includes first and second pulse injection units for providing high frequency perturbation of the exhaust gasses as well as a second, lower frequency periodic perturbation.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, a jet noise suppressor is provided to effectively suppress the exhaust noise that emanates from a gas turbine engine during operation. The jet noise suppressor of the present invention has particular utility in aircraft applications where effective noise suppression is particularly desirable.
The jet noise suppressor of the present invention includes a pair of high frequency pulse injection units mounted exteriorly of the exhaust nozzle of the gas turbine engine. Each pulse injection unit has an outlet directed such that it discharges into the boundary of the flow of exhaust gasses from the turbine engine during operation. The pulse injection units are located oppositely from one another, diametrically across the exhaust nozzle.
Each pulse injection unit includes a resonance tube placed in outlet fluid communication with an injector nozzle. The outlet of the injector nozzle is directed into the flow of exhaust gasses as described above.
The jet noise suppressor includes a pair of high pressure gas sources, each of which can be an air compressor or an engine compressor discharge port. The high pressure gas generated by the first source is directed through suitable conduit or tubing into each of the resonance tubes. Resonance tubes are known, and in general, are fluidic devices that receive a pressurized fluid input and provide a pulsating fluid output. The nature of the output, such as pulse frequency and amplitude is variable and depends on upon the dimensions of the resonance tube.
As stated, each pulse injection unit includes a resonance tube in outlet fluid communication with an injector nozzle. Each injector nozzle receives high pressure gas from a second source. The pulsating fluid output of the resonance tube, as directed into the injector nozzle perturbs the flow of air therein, effectively breaking it up into discrete slugs or pulses which exit the nozzle and are directed into the exhaust stream. It is believed that this pulsating flow from the injector nozzle destroys large coherent vorticular structures by introducing high levels of small scale mixing.
According to an important aspect of the present invention, the second source of high pressure gas includes a flip-flop type actuator for switching the inlet flow to the injector nozzles alternately between the first and second pulse injection units. This provides for dramatic noise suppression as well as exhaust temperature reduction by introducing a low frequency, high amplitude modulation into the flow of exhaust gas. This has the overall effect of reducing broadband turbulent mixing noise in the exhaust by starving the low frequency disturbances of energy. Moreover, high levels of ambient air are entrained in the exhaust, lowering its temperature.
Advantageously, the jet noise suppressor of the present invention has no moving parts, enhancing reliability as well as reducing costs. The jet noise suppressor, by virtue of its simplicity and autonomous operating capability can be retrofit into a wide variety of aircraft. And, the jet noise suppressor includes no structure to impede the flow of exhaust gasses from the engine.